Electrochemical energy source and electronic device incorporating such an energy source

ABSTRACT

The invention relates to an electrochemical energy source comprising at least one fuel cell, which fuel cell comprises: a first current collector coupled to a negative electrode, a fuel source connected to said negative electrode, a second current collector coupled to a positive electrode, an oxidant source connected to said positive electrode, and an ion-conducting electrolyte located between said negative electrode and said positive electrode. The invention also relates to an electronic device incorporating such an electrochemical energy source.

The invention relates to an electrochemical energy source comprising atleast one fuel cell, which fuel cell comprises: a first currentcollector coupled to a negative electrode, a fuel source connected tosaid negative electrode, a second current collector coupled to apositive electrode, an oxidant source connected to said positiveelectrode, and an ion-conducting electrolyte located between saidnegative electrode and said positive electrode. The invention alsorelates to an electronic device incorporating such an electrochemicalenergy source.

An electrochemical energy source comprising a fuel cell is known in theart. In principle, a fuel cell operates like a battery. However, unlikea battery, a fuel cell commonly neither degenerates (if fuel and oxidantare constantly added to the fuel cell) nor requires electricalrecharging. A fuel cell will produce energy (substantially) in the formof electricity and heat as long as fuel and oxidant are supplied to thefuel cell. There are several advantages in the use of a fuel cell ascompared with a battery. A major advantage of the fuel cell can be thatthe capacity is much higher than the capacity of a conventional battery.Moreover, a fuel cell is a relatively clean energy source. Primarily,depending on the nature of the fuel used, only water vapor and carbondioxide (on using fuels containing carbon) are evolved during theelectrochemical conversion process.

A conventional battery integrated in a part of a housing of anelectrical appliance is disclosed in the American patent publicationU.S. Pat. No. 5,180,645. An integrated battery (permanently) built intoor forming part of an equipment housing has numerous advantages. Anintegrated battery results commonly in a smaller overall size, lighteroverall weight, and lower fabrication cost of the electronic device.Besides these advantages, however, the known electrochemical energysource which is integrally formed with a part of a housing of anelectronic device has several drawbacks. One of the drawbacks is therelatively restrictive degree of freedom of design since the choice of adesirable shape and/or format is extremely limited, i.e. restricted tothat of flat batteries. Therefore the shape of the housing of saidelectronic device is commonly adapted to the shape and format ofbatteries suitable for that specific device.

It is an object of the present invention to provide an improvedelectrochemical energy source comprising at least one fuel cell, whichenergy source can be applied in an electronic device having an arbitraryshape and thus without incurring the described drawback while preservingthe advantages of the prior art.

The object is achieved by an electrochemical source as described in thepreamble and characterized in that the electrochemical energy source hasa curved, planar geometry. A major advantage of the electrochemicalenergy source having a curved, planar geometry is that any desired shapeof said electrochemical energy source can be realized so that thefreedom of choice as regards shape and format of said electrochemicalenergy source is many times greater than the freedom offered by thestate of the art. The geometry of said electrochemical energy source canthus be adapted to spatial limitations imposed by any electricalapparatus in which the battery can be used, contrary to the techniquesknown of the prior art. From a point of view of space, electricalapparatuses can now be more efficiently configured in many cases becauseof the greater freedom of choice of the geometry of the electrochemicalenergy source; this may lead to a saving of space in and a greaterfreedom of design of the apparatus. It is to be noted that the curvedplanar geometry results in a curved battery which has a curved planarshape which may be concave/convex or wavy. However, it also imaginablefor a person skilled in the art to apply an angular energy source whichhas a hooked shape.

In a preferred embodiment, the electrochemical energy source comprises alamination of said anode and said cathode, characterized in that thelamination has a curved shape such that the lamination is situated inone curved plane. Relatively thin and elongated laminations can thus beprovided in an relatively simple manner.

Preferably, the electrolyte is formed by a Proton Exchange Membrane(PEM). The PEM, being a solid-state electrolyte, provides transport ofprotons from the negative electrode to the positive electrode. Theoperating temperature of the PEM is commonly up to 120° C. Depending onthe application of the fuel cell, different types of electrolytes may beused. Besides PEM, for example alkaline (AFC), phosphoric acid (PAFC),molten carbonate (MCFC), and solid oxide (SOFC) may also be used aselectrolytes. In another preferred embodiment, said electrolyte is aliquid-state electrolyte, in particular alkaline, phosphoric acid, andmolten carbonate, retained in a matrix located between the positiveelectrode and the negative electrode. The matrix may also varyindependence on the type of electrolyte used in the fuel cell. Foralkaline usually asbestos is used as a matrix, for phosphoric acidsilicon carbide may be used, and for molten carbonate a ceramic matrixof LiAlO₂ is commonly used.

In a preferred embodiment, the electrochemical energy source comprisesat least one assembly of fuel cells electrically coupled together,wherein insulation means are provided for insulating one cell withinsaid assembly from another cell within said assembly. Said fuel cellsmay be connected in parallel to increase total power output, and/or inseries to increase the voltage produced by the fuel cells.

In another preferred embodiment, cooling means are provided for coolingsaid fuel cell. The cooling means are suited to control the heatproduced by said fuel cell. Said cooling means may be formed, forexample, by a plate, a flexible material layer, or tubes commonlycontaining cooling liquid.

Preferably, the electrochemical energy source comprises at least onebattery electrically coupled to said fuel cell. Integration of fuelcells with batteries or supercapacitors leads to so-called hybridsystems or hybrid energy sources. A first advantage of said hybridsystem is that a high-load performance can be achieved. In situationswhere a relatively high power output has to be generated, both thebattery and the fuel cell may be brought into action. Another advantageof the hybrid system is that the system can be started up easily atrelatively low temperatures by bringing the battery into action. Unlikea battery, a fuel cell per se commonly functions relatively tardily atlow temperatures.

The positive electrode and the negative electrode are preferablyprovided with a catalyst for accelerating electrochemical reaction insaid fuel cell. The type of electrocatalyst commonly depends on the typeof electrolyte used. In case of a PEM or a PAFC, platinum is mostly usedas electrocatalyst. In an AFC a wide range of electrocatalysts may beused, for example nickel, silver, metal oxides, spinels, noble metals,and mixtures of these.

In a preferred embodiment, said fuel cell is stacked by a polymerdeposited in cavities formed in the positive electrode, the negativeelectrode and the electrolyte. In this way the fuel cells are formed bythe so-called “Lithylene” technology. This “Lithylene” technology isdescribed in more detail in the American patent publication U.S. Pat.No. 6,432,576. In this technology, the active material layers themselvesare not embedded in a polymer, but the polymer is used exclusively forbinding material layers together. Binding the positive electrode and thenegative electrode is commonly important in fuel cells, as the operationtemperature of the fuel cell can vary over a wide range, therebyexpanding and shrinking components of the fuel cell significantly. Solidelectrical contact must be maintained between all components within thefuel cells at every temperature. Polymeric riveting of all layers of thefuel cell can cause this solid contact to be maintained between catalystlayers and the electrolyte. The viscosity of the polymer must besufficient low to allow good filling of empty spaces within the fuelcell in such a way that leakage of the fuel is prevented. The“Lithylene” technology is particularly advantageous with assemblies(“stacks”) of fuel cells as the assembly can obtain a relatively goodmechanical strength by riveting of the components of said assembly. Thepolymeric material is shaped so as to fit the shapes of the respectiveholes (cavities), thereby sticking the positive electrode, negativeelectrode, and electrolyte together. The shape of said assembly can bemaintained in a relatively easy and simple way through riveting of saidassembly. It is important to retain a good supply of fuel and oxidant tothe respective electrodes, despite the fact that the components areriveted by polymer.

The invention also relates to an electronic device incorporating such anelectrochemical energy source. Preferably the electronic devicecomprises a housing incorporating said electrochemical energy source.Advantages of the application of a electrochemical energy source with aplanar, curved geometry in said housing of an electrical device havealready been described above.

The invention will be described in detail hereinafter with reference tothe non-limitative embodiments that are shown in the Figures.

FIG. 1 is a schematic view of the working principle of a fuel cell,

FIG. 2 is a perspective and overall view of the enclosure of anelectrochemical energy source in accordance with the invention, and

FIG. 3 is a perspective view of a shaver provided with anelectrochemical energy source in accordance with the invention.

FIG. 1 is a schematic view of the working principle of a fuel cell 1.The fuel cell 1 comprises a positive electrode 2, a negative electrode3, and a solid-state electrolyte 4 positioned between the positiveelectrode 2 and the negative electrode 3. In this particular embodimentthe (solid-state) electrolyte 4 is formed by a Proton Exchange Membrane(PEM), which provides transport of protons from the negative electrode 3to the positive electrode 2. The positive electrode 2 is connected to anoxidant source A and an excess oxidant and reaction product outlet B,whilst the negative electrode 3 is connected to a fuel source C and anexcess fuel outlet D. In this particular embodiment (gaseous) hydrogenis used as the fuel and (atmospheric) oxygen is used as the oxidant. Thepositive electrode 2 and the negative electrode 3 are electricallyconnected to an electronic device 5. During use, the hydrogen will reacton the negative electrode 3 thereby creating protons and electrons. Theprotons will be conducted via the PEM to the positive electrode 2 whilethe electrons will be transported via the electronic device 5 to saidpositive electrode 2. On the positive electrode 2 the oxygen will reactwith the received protons and electrons, thereby forming water as areaction product. The excesses or unused fractions of hydrogen andoxygen added to the fuel cell 1 may preferably be recirculated and maybe re-added to the fuel cell via inlet A and inlet C, respectively. Thepositive electrode 2, negative electrode 3, and electrolyte 4 arestacked by polymer material 9 pierced (riveted) through these components2, 3, 4 according to the “Lithylene” technology. In this way amechanically stable fuel cell I can be generated.

FIG. 2 is a perspective view of an electrochemical energy source 6 inaccordance with the invention. The electrochemical energy source 6comprises one or more, preferably laminated, fuel cells. FIG. 2 clearlyshows that the electrochemical energy source 6 has an (arbitrarilychosen) curved, planar shape.

FIG. 3 is a perspective view of a shaver 7 which is provided with anelectrochemical energy source 8 in accordance with the invention. Theelectrochemical energy source 8 has a curved shape such that it can beoptimally accommodated in the housing of the shaver 7. The geometry ofthe electrochemical energy source 8 may be chosen in conformity with therequirements imposed by an electrical device, for example the shaver 7,in such a manner that the space available in the electrical apparatuscan be used to receive the electrochemical energy source 8.

1. Electrochemical energy source, comprising a plurality of fuel cells,wherein each fuel cell comprises: a first current collector coupled to anegative electrode, a fuel source connected to said negative electrode,a second current collector coupled to a positive electrode, an oxidantsource connected to said positive electrode, and an ion-conductingelectrolyte located between said negative electrode and said positiveelectrode, characterized in that the electrochemical energy source has acurved, planar geometry, wherein at least one fuel cell is stacked by apolymer material riveted through cavities formed in the positiveelectrode, the negative electrode, and the electrolyte, and wherein theelectrochemical energy source comprises a lamination of at least one ofsaid positive electrodes and said negative electrodes, characterized inthat the lamination has a curved shape such that the lamination issituated in one curved plane and the resulting electrochemical energysource has a corresponding curved surface.
 2. Electrochemical energysource according to claim 1, characterized in that said electrolyte isformed by a Proton Exchange Membrane (PEM).
 3. Electrochemical energysource according to claim 1, characterized in that said electrolyte is aliquid-state electrolyte retained in a matrix located between thepositive electrode and the negative electrode.
 4. Electrochemical energysource according to claim 1, characterized in that the electrochemicalenergy source comprises at least one assembly of fuel cells electricallycoupled together, wherein insulation means are provided for insulatingone cell within said assembly from another cell within said assembly. 5.Electrochemical energy source according to claim 1, characterized inthat cooling means are provided for cooling said fuel cell. 6.Electrochemical energy source according to claim 1, characterized inthat the electrochemical energy source comprises at least one batteryelectrically coupled to at least one of said fuel cells. 7.Electrochemical energy source according to claim 1, characterized inthat the positive electrode and the negative electrode are provided witha catalyst for accelerating electrochemical reaction in said fuel cell.8. Electronic device incorporating an electrochemical energy sourceaccording to claim
 1. 9. Electronic device according to claim 8,characterized in that the electronic device comprises a housingincorporating said electrochemical energy source.